Toroidal continuously variable transmissions transmit motive power through an arrangement in which a power roller is tightly held between an input disk and an output disk. Rotations from the input disk rotate the power roller which in turn rotates the output disk as a result of frictional contact.
The transmission of motive power under these circumstances depends on the force of frictional contact between the input/output disks and the power roller. The frictional force in turn corresponds to a thrust force which grips (sandwiches) the power roller. U.S. Pat. No. 2,959,063 discloses a mechanism of generating a thrust force which acts on the input/output disks in order to grip the power roller.
The disclosed mechanism consists of arranging a plurality of cam rollers held in a retainer on the same axis as the input/output disks to generate a thrust force so that the power roller which is gripped between the input/output disks is placed under pressure in proportion to the input torque from the input shaft.
The plurality of cam rollers are disposed on the inner side of the retainer at equal intervals in the radial direction. Each cam roller is formed in an approximately conical trapezoid shape and is disposed so that the long radius end faces outwardly. The end face of each cam roller forms a rounded face which is maintained in contact with the inner face of the retainer.
Due to the fact that the long radius end faces are maintained in contact by the retainer, the cam rollers are gripped between a cam flange(input member), which is a member fixed on the input shaft side, and the rear face of the input disk, which can slide with respect to the input shaft. A cam face, the depth of which gradually decreases towards the circumference, is formed on the opposed faces of the input member and rear face of the input disk. When the input member rotates in response to an input torque, the cam roller displaces through a narrow range along the cam face towards the circumference while rotating. The input disk is pressured in the axial direction from the rear face and, in this way, a thrust force is generated. The thrust force allows the input disk to press the power roller onto the output disk and thus to achieve the transmission of rotational torque.
The conical trapezoid shape of the cam roller allows it to be pressured in the radial direction by the rotations of the input member. As a result, a sliding friction is generated on the metal contact face of the long radius end face of the cam roller and the retainer. Surface pressure acting on the cam roller decreases away from the center of the contact point of the rounded long radius end face with the inner face of the retainer. In this way, the moment of the sliding frictional force which impedes the cam roller from rotating can be minimized.